After Sir Keir Starmer, Britain’s prime minister, hailed the “remarkable breakthrough” in talks between the US and Ukraine, his allies were quick to highlight the key role played behind the scenes by Jonathan Powell, an architect of the Northern Ireland peace process.

Downing Street’s national security adviser — a veteran of the Tony Blair era — has been deployed to help smooth discussions that only days earlier had completely broken down.

Powell, Blair’s chief of staff for a decade at Number 10, is revered in Whitehall circles for the role he played in brokering peace in Northern Ireland: shadowy talks with hard line protagonists in Northern Ireland led to the 1998 Good Friday Agreement.

Starmer — who hosts a video meeting of leaders from about two dozen countries from a “coalition of the willing” on Saturday — has turned to Powell to try to win US military support for a UK-French led peace guarantee force in Ukraine, an equally daunting task.

Powell has already racked up serious air miles and forged many of the relationships he needs, crossing the Atlantic several times in recent months to meet US counterpart Mike Waltz and other senior figures in the Trump administration.

Last weekend Powell travelled to Kyiv to meet Ukrainian President Volodymyr Zelenskyy and his chief of staff Andriy Yermak to work on a written proposal to bridge the gap between Ukraine and the US.

British officials said the talks focused on a ceasefire, confidence building measures including for the exchange of prisoners of war, the release of detained civilians and the return of children.

Ukraine also agreed to sign a minerals deal with the US, and Zelenskyy crucially bent the knee to Trump, thanking the US for its support and embracing the Washington peace plan that British officials admit is “the only game in town”.

This Friday, Powell will again fly to Washington to try to persuade Waltz that the Trump administration must play a security “backstop” role to ensure a lasting peace in Ukraine.

The aim is for a ceasefire to usher in a staged negotiation that would include a truce on land and sea, and eventually British and French troops among international forces helping to guarantee the peace at strategic locations away from the disputed territory.

Powell will talk through the plan with European counterparts and Waltz on Friday.

Similar talks in Washington earlier this month between UK defence secretary John Healey and US equivalent Pete Hegseth ended without any agreement.

Without US intelligence, surveillance and air cover, Starmer has warned that a European force in Ukraine will not be able to deter Vladimir Putin from “coming again”. Yet so far Trump has shown no sign of obliging.

“It’s a crapshoot,” said one British official, when asked to guess what Trump might do next. Another said: “It would be wrong to say that there has been any movement on a US backstop but we are still talking.”

However, even getting to this point has been a diplomatic achievement. After Zelenskyy’s Oval Office bust-up with Trump at the end of last month, there was despair in London about the prospects for peace.

“He stupidly walked into a trap,” said one UK official, noting that Zelenskyy had failed to heed British and French advice to use gratitude and flattery to win over Trump. Both French President Emmanuel Macron and Starmer had deployed those tactics in more successful meetings with Trump earlier in the week.

Since that confrontation Powell — who founded the charity Inter Mediate in 2011 to build on his experience in negotiating peace in Northern Ireland — has been advising Zelenskyy on how to repair the damage.

Powell has been at pains to tell colleagues that this is very much a joint effort with his so-called E3 counterparts from Germany and France, who will also meet Waltz in Washington on Friday, but his experience is seen as vital.

Powell, whose talent at self-deprecation is a valuable diplomatic tool, makes light of the experience he brings to the job. “We managed with youth last time,” he tells colleagues, noting that when he started working for Blair in the 1990s he was aged just 38.

Powell first travelled to Washington last December with Morgan McSweeney, Sir Keir Starmer’s chief of staff, for talks with Trump’s transition team.

Last month he returned to the US capital to discuss a raft of issues with Waltz, including the UK’s proposed deal with Mauritius on the future of the Chagos Islands, which has a security implication for a crucial joint US-UK military base on the atoll of Diego Garcia. 

Powell was the UK prime minister’s special envoy on the negotiations with Mauritius before Starmer made him national security adviser.

His deal was widely criticised by the Conservative opposition in Britain — but criticism has subsided after it was publicly endorsed by Trump in the Oval Office last month when he met Starmer.

Blair’s former political secretary John McTernan, who worked closely with Powell when he was the Downing Street chief of staff, recalled his pivotal role in the Northern Ireland peace process and said he was “as modest as he is effective”.

He added that Powell’s “political smarts, his humour, and his personal modesty combined with his diplomatic experience are the reason he has made such an impact . . . so quickly”.